ProtologueSp. pl. 2: 991 (1753).FamilyAmaranthaceae Chromosome number2n = 34Vernacular namesSpiny amaranth, prickly amaranth, spiny pigweed (En). Amarante épineuse, épinard malabar, épinard piquant (Fr). Amaranto, bredo (Po). Mchicha (Sw).Origin and geographic distributionAmaranthus spinosus originates probably from lowland tropical South and Central America and was introduced into other warmer parts of the world from about 1700 AD onwards. At present it occurs in all tropical and subtropical regions, including tropical Africa, often gregariously and as a weed. It is sometimes found in temperate zones as well. It is rarely cultivated.UsesIn tropical Africa and elsewhere Amaranthus spinosus leaves and young plants are collected for home consumption as a cooked, steamed or fried vegetable, especially during periods of drought. Leaves are occasionally found for sale on markets. In Uganda and Kenya it commands a lower price than, for example, Amaranthus dubius Mart. ex Thell. because of its spines and because it is not much liked. Its use is declining, and it is acquiring the status of a famine food. It has a bitter taste and is usually eaten in small quantities as a substitute when no other vegetables are available. Amaranthus spinosus is also used as forage and said to increase the yield of milk in cattle. However, the spines can cause injury to the mouths of grazing animals and cases of poisoning in cattle have also been reported.In Uganda the ash of burnt Amaranthus spinosus plants is used as a tenderizer in cooking tough vegetables such as cowpea leaves and pigeon peas. The ash is also used as a vegetable salt and in southern Africa it is used as a snuff, alone or with tobacco.Amaranthus spinosus has numerous medicinal uses. The root is known as an effective diuretic. In South-East Asia a decoction of the root is used to treat gonorrhoea and is also applied as an emmenagogue and antipyretic. In many countries, including those in Africa, the bruised leaves are considered a good emollient and applied externally in cases of eczema, burns, wounds, boils, earache and haemorroids. The plant ash in solution is used to wash sores. Plant sap is used as an eye wash to treat ophthalmia and convulsions in children. In Malaysia Amaranthus spinosus is used as an expectorant and to relieve breathing in acute bronchitis. In mainland South-East Asia, it is also used as a sudorific, febrifuge, antidote to snake poison, galactagogue, and to treat menorrhagia. Some tribes in India apply Amaranthus spinosus to induce abortion.PropertiesThe nutritional value of Amaranthus spinosus is comparable to that of other vegetable amaranths. Amaranthus leaves contain per 100 g edible portion: water 84.0 g, energy 176 kJ (42 kcal), protein 4.6 g, fat 0.2 g, carbohydrate 8.3 g, fibre 1.8 g, Ca 410 mg, P 103 mg and Fe 8.9 mg (Leung, W.-T.W., Busson, F. & Jardin, C., 1968). Cases of spontaneous poisoning in cattle by Amaranthus spinosus have been reported, particularly after severe droughts when few other forages were available. It was suggested that Amaranthus spinosus caused renal failure. The roots contain α-spinasterol and some saponins. Sterols, n-alkanes, fatty acids and free alcohols have been found in petroleum-ether extracts of the herb. The flavonoid rutin has been found in the aboveground parts in a concentration of up to 1.9%, and traces of hydrocyanic acid in the leaves. The considerable amount of potassium in the leaves might explain the diuretic properties. A lectin has been isolated from the seeds. Its reaction was non-specific in general: it reacted with human and various animal erythrocytes. Its unique carbohydrate specificity will prove useful in biochemistry.Amaranthus spinosus possesses a strong phagocytic effect. No antibacterial activity has been demonstrated, but crude aqueous extracts showed fungicidal activity against Cercospora cruenta, which causes a leafspot disease in mung bean (Vigna radiata (L.) Wilczek). They showed antiviral activity against Aujeszky virus (ADV) in IB-RS-2 pig cell cultures and bovine diarrhoea virus (BVDV) in GBK bovine cell lines. The antiviral activity against BVDV, however, was lost upon heating the extract.Allelochemicals have been isolated and identified from aerial plant parts. These are volatile aliphatic compounds which inhibit germination of seeds of crops like carrot, tomato and onion.BotanyAnnual, erect, monoecious herb, up to 100(–130) cm tall, much branched; stem terete or obtusely angular, glabrous or slightly pubescent, green or variably suffused with purple. Leaves alternate, simple; stipules absent; petiole approximately as long as leaf-blade; blade ovate -lanceolate to rhomboid, 3.5–11 cm × 1–4.5 cm, acute and often slightly decurrent at base, obtuse, rounded or slightly retuse and often short mucronate at apex, entire, glabrous or slightly pubescent on veins when young. Inflorescence consisting of dense clusters, lower ones axillary, higher ones often collected in an axillary and terminal spike which is often branched in its lower part; axillary clusters usually armed with (1–)2(–3) very sharp spines up to 2 cm long. Flowers unisexual, solitary in the axil of a bract, subtended by 2 bracteoles; bracts and bracteoles scarious, mucronate from a broad base, shorter or as long as the perianth; male flowers usually arranged in a terminal spike above the base of the inflorescence, green; tepals 5 or in male flowers often 3, free, subequal, ovate-oblong to oblong-spatulate, up to 2.5 mm long, very convex, membranous, with transparent margins and green or purple median band; male flowers with 5 stamens about as long as tepals; female flowers with superior, oblong ovary, 1-celled, styles 2–3, ultimately recurved. Fruit an oblong capsule with persisting styles, circumscissile a little below the middle or indehiscent, 1-seeded. Seed about 1 mm in diameter, shiny black or brownish -black with thin margin. Seedling with epigeal germination; cotyledons leafy, glabrous, apex rounded to slightly acute; hypocotyl up to 12 mm long, epicotyl absent.Amaranthus comprises about 70 species, of which about 40 are native to the Americas. It includes at least 17 species with edible leaves. It is almost impossible to make a distinction between Amaranthus spinosus and Amaranthus dubius Mart. ex Thell. based on morphological characters; Amaranthus spinosus has axillary spines which are not present in Amaranthus dubius. However, spineless Amaranthus spinosus plants with 2n = 34 have been observed in several localities. In Nigeria an Amaranthus dubius plant with 2n = 32 has been recorded; this might be a spineless Amaranthus spinosus. Other more or less reliable differences are the greater number of terminal male flowers in the inflorescences of Amaranthus spinosus and the smaller pores of the pollen.Seeds mature about one month after flowering. They are scattered around the mother plants or distributed by animals feeding on the plants. It has been observed that large numbers of seedlings emerge from decaying cattle faecal deposits. Seeds are eaten by birds.EcologyAmaranthus spinosus is adapted to a wide range of climatic and edaphic factors. It grows best in the sun or in light shade; a light intensity of less than 30% completely suppresses flowering. Flowering is earliest and most abundant in areas with daylengths of 11–12 hours. Spiny amaranth is nitrophilous and prefers soils with a high organic matter content, but is also able to grow on sandy soils. Optimal growth is obtained on soils with moderate moisture content, but Amaranthus spinosus is capable of growing on wet soils as well. It is drought-resistant and can even grow under arid conditions.Spiny amaranth is a very noxious weed in many parts of the world. It is, for instance, troublesome in maize, cassava and groundnut in Ghana, in cotton in Mozambique, and in sugar cane in South Africa. In general, it is very common in roadsides, waste places, railway yards, cropped land and gardens, up to 1400 m altitude.ManagementAmaranthus spinosus is propagated by seed. Some types are known to produce 235,000 seeds per plant. The weight of 1000 seeds is 140–250 mg. Freshly collected seeds may germinate at temperatures as high as 40°C, with a germination rate of up to 95%. After storage, however, temperature requirements are lower. Seeds stored for one month at room temperature have almost 100% germination, and after 5 months they have approximately 90% germination. When they are stored for one year at 20°C the germination rate will drop to about 50%, but storage at lower temperatures gives a higher rate. Seedlings often exhibit a high degree of mortality. For use as a vegetable, the plants are mostly collected while still young before the spines have hardened.As a weed in tomato in India, spiny amaranth has been successfully controlled by the application of geraniol, which completely blocked the germination of the weed without affecting the tomato crop. An ethanolic extract of seeds of Coffea arabica L. (with 1,3,7-trimethylxanthine as active ingredient) at a concentration of 1.2 g/l, completely inhibited germination of spiny amaranth in a crop of black gram (Vigna mungo (L.) Hepper) without negative effects to this pulse crop.Amaranthus spinosus is a host plant for, among others, tobacco mosaic virus, groundnut rosette virus, cucumber mosaic virus and root-knot nematodes (Meloidogyne spp.), which attack some commercial crops. When the world’s worst weeds are ranked on the basis of the number of pests hosted, Amaranthus spinosus is placed number 6, hosting 15 pests that may affect crops. Some insects attacking Amaranthus spinosus have been recorded from Mexico: the pyralid Herpetogramma bipunctalis and the curculionid Conotrachelus seniculus. These might be useful for biological control.Genetic resources and breedingThe genetic variability of Amaranthus spinosus is great because of its large area of distribution and its wide ecological adaptation. A collection of amaranths is kept at the Rodale Organic Gardening and Farming Research Center (OGFRC) at Kutztown, Pennsylvania, United States; South-East Asian accessions are kept at the Asian Vegetable Research and Development Center (AVRDC) at Tainan, Taiwan. African cultivars and introductions from OGFRC are kept at the National Horticultural Research Institute (NHR) in Nigeria and African cultivars at the AVRDC centre at Arusha, Tanzania. Indian collections are kept at the National Bureau of Plant Genetic Resources (NBPGR), New Delhi, India. Many national institutes have small working collections of local cultivars. Evaluation and variability studies are needed to reveal the amount of exploitable genetic variation.ProspectsDespite the reputed high nutritional value of the leaves, Amaranthus spinosus most probably will remain a famine vegetable and forage because of the rather poor taste and the spines. The medicinal properties of Amaranthus spinosus have received little attention. The diuretic and anti-inflammatory properties in particular deserve more research, as these properties are valued in many different regions of the world.Major references• Burkill, H.M., 1985. The useful plants of West Tropical Africa. 2nd Edition. Volume 1, Families A–D. Royal Botanic Gardens, Kew, United Kingdom. 960 pp. • Katende, A.B., Ssegawa, P. & Birnie, A., 1999. Wild food plants and mushrooms of Uganda. Technical Handbook No 19. Regional Land Management Unit/SIDA, Nairobi, Kenya. 490 pp. • Lemmens, R.H.M.J. & Bunyapraphatsara, N., 1999. Amaranthus spinosus L. In: de Padua, L.S., Bunyapraphatsara, N. & Lemmens, R.H.M.J. (Editors). Plant Resources of South-East Asia No 12(1). Medicinal and poisonous plants 1. Backhuys Publishers, Leiden, Netherlands. pp. 110–113. • Maundu, P.M., Ngugi, G.W. & Kabuye, C.H.S., 1999. Traditional food plants of Kenya. Kenya Resource Centre for Indigenous Knowledge (KENRIK), Nairobi, Kenya. 270 pp. • Ruffo, C.K., Birnie, A. & Tengnäs, B., 2002. Edible wild plants of Tanzania. Technical Handbook No 27. Regional Land Management Unit/ SIDA, Nairobi, Kenya. 766 pp.Other references• Burkill, H.M., 2000. The useful plants of West Tropical Africa. 2nd Edition. Volume 5, Families S–Z, Addenda. Royal Botanic Gardens, Kew, United Kingdom. 686 pp. • CSIR, 1985. The wealth of India. A dictionary of Indian raw materials and industrial products. Raw materials. Revised Edition. Volume 1. Publications and Information Directorate, New Delhi, India. 513 pp. • Gopal, B., 1974. Autecological study of Amaranthus spinosus L. Annals of Arid Zone 13(3): 187–195. • Koseki, I., Simoni, I.C., Nakamura, I.T., Noronha, A.B. & Costa, S.S., 1990. Antiviral activity of plant extracts against aphthovirus, pseudorabies virus and pestivirus in cell cultures. Microbios Letters 44(173): 19–30. • Leung, W.-T.W., Busson, F. & Jardin, C., 1968. Food composition table for use in Africa. FAO, Rome, Italy. 306 pp. • Oliveira, J.S. & de Carvalho, M.F., 1975. Nutritional value of some edible leaves used in Mozambique. Economic Botany 29(3): 255–263. • Schippers, R.R., 2000. African indigenous vegetables. An overview of the cultivated species. Natural Resources Institute/ACP-EU Technical Centre for Agricultural and Rural Cooperation, Chatham, United Kingdom. 214 pp. • Stevels, J.M.C., 1990. Légumes traditionnels du Cameroun: une étude agrobotanique. Wageningen Agricultural University Papers No 90-1. Wageningen University, Wageningen, Netherlands. 262 pp. • Townsend, C.C., 1985. Amaranthaceae. In: Polhill, R.M. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. 136 pp. • Townsend, C.C., 1988. Amaranthaceae. In: Launert, E. (Editor). Flora Zambesiaca. Volume 9, part 1. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 28–133.Sources of illustration• Lemmens, R.H.M.J. & Bunyapraphatsara, N., 1999. Amaranthus spinosus L. In: de Padua, L.S., Bunyapraphatsara, N. & Lemmens, R.H.M.J. (Editors). Plant Resources of South-East Asia No 12(1). Medicinal and poisonous plants 1. Backhuys Publishers, Leiden, Netherlands. pp. 110–113.Author(s)